Oxidation catalyst containing vanadium and titanium



United States Patent US. Cl. 252-469 11 Claims ABSTRACT OF THEDISCLOSURE A catalyst for the gas phase oxidation of aromatichydrocarbons or unsaturated aliphatic hydrocarbons into carboxylc acidswhich consists essentially of an inert nonporous carrier coated to athickness of about 0.02 to 2 mm. with a composition of 1 to 15% byweight of vanadium pentoxide and 85 to 99% by weight of titaniumdioxide, the catalyst having a content of vanadium pentoxide of 0.05 to3% by weight. The catalyst is particularly useful for the oxidation ofo-xylene to phthalic acid and permits high yields at high spacevelocities in contact with a catadlyst in which the vanadium content isquite small.

Many catalysts have already been proposed for the oxidation of aromatichydrocarbons and unsaturated aliphatic hydrocarbons to carboxylic acids.Almost all these catalysts contain vanadium compounds as the activeconstituent, with activating additions of metal oxides, such as theoxides of zinc, cerium, chromium, titanium, boron, zirconium, bismuth,tungsten, lead and cobalt or also compounds of silver, copper, nickel orphosphorus. Alkali metal compounds and alkaline earth metal compoundshave also been used as additives.

None of the catalysts described is however entirely satisfactory incarrying out oxidation reactions on a commercial scale. The yields areusually unsatisfactory, particularly with high conversions of thestarting material. In many cases the catalyst will permit only low spacevelocities. The life of the catalysts is also often unsatisfactory.

The object of the present invention is to provide a catalyst containingvanadium and titanium which permits the oxidation of aromatichydrocarbons and unsaturated aliphatic hydrocarbons to carboxylic acidsin good yields with high conversions, and with which high spacevelocities are possible and which has a long life.

This and other objects are achieved in accordance with this inventionwith a catalyst containing vanadium and titanium for the oxidation ofaromatic hydrocarbons and unsaturated aliphatic hydrocarbons tocarboxylic acids, in which an inert nonporous carrier is coated with alayer of a composition 0.02 to 2 mm. thick which contains l to 15% byweight of vanadium pentoxide and 85 to 99% by Weight of titaniumdioxide, the catalyst having a content of vanadium pentoxide of lessthan 3% by weight.

The new catalyst enables hydrocarbons to be oxidized to form carboxylicacids in particularly high yields. In particular the proportion ofby-products resulting from the oxidation reaction proceeding too far(combustion) is low. Excellent yields may be obtained even when thestarting material is practically entirely converted. The catalystpermits particularly high space velocities and exhibits practically noloss in activity even after operation for very long periods. In fact theyield in prolonged operation often even rises for example by 2 to 5%.

3,464,930. Patented Sept. 2, 1969 "Ice The catalyst is suitable for manyof the prior art oxidation reactions of aromatic hydrocarbons andunsaturated aliphatic hydrocarbons to form carboxylic acids. Goodresults are obtained in the oxidation of olefinically unsaturatedhydrocarbons which in particular'have three to five carbon atoms and oneor two olefinic double bonds, for example in the oxidation of propyleneto acetic acid and in the oxidation of butene-(l), butene-(Z) orbutadiene-(l,3) to maleic acid. Suitable aromatic hydrocarbons which areconverted by oxidation into carboxylic acids preferably contain six totwelve carbon atoms, such asbenzene which is oxidized to form maleicacid, naphthalene which is oxidized to form phthalic acid, and benzenesand naphthalenes bearing one to four methyl groups as substituents, suchas toluene, which is oxidized to form benzoic acid, ocorfl-methylnaphthalene which is converted by oxidation into aorB-naphthoie acid, and durene which is oxidized to form pyromelliticacid. Particularly good results are obtained in the oxidation ofo-xylene to phthalic acid. The catalyst permits high space velocitiesand, for example, in the production of phthalic anhydride gives a yieldby weight of more than 100% even at a space velocity of 10,000 times thevolume of reaction mixture per unit volume of catalyst per hour.

Nonporous, inert materials are used as catalysts, i.e., materials freefrom pores or having a small surface area, preferably less than 3 sq.m./g., advantageously 0.005 to 2 sq. m./g., such as quartz or silicicacid or particularly porcelain, fused aluminum oxide, silicon carbideand fused or sintered silicates, for example aluminum silicate,magnesium silicate, zinc silicate and zirconium silicate andparticularly steatite. Both synthetic and natural materials may be used.The carrier for the catalyst advantageously has a mean particle size offrom 2 to 10 mm. and is preferably used in the form of spheres, pelletsor cones.

Sometimes, it is advantageous to roughen the surface of smooth carriersto a slight extent prior to their use by etching, for example withhydrofluoric acid, gaseous hydrogen fluoride, or ammonium fluoridesolution, in order to improve adhesion of the active composition.

It is often an advantage to prime, precoat or pretreat the carrier with0.05 to 1.5% by weight, particularly 0.1 to 1% by weight, of an oxide ofthe metals vanadium, molybdenum, tungsten, chromium, titanium or iron ora mixture of these oxides prior to coating the carrier with thecomposition containing vanadium pentoxide and titanium dioxide. For thispurpose the said oxides (or compounds of the said metals which areconverted by heating into the oxides) as melts or preferably in solutionare brought into contact with the carrier so that a uniform layer formson the carrier. The metal compounds are advantageously used dissolved inwater, ammonium thiocyanate or an organic solvent, such as urea,thiourea or alcohols. In order to achieve adequate strength of thepriming, and in order to achieve good adhesion of the subsequentcoating, it is advantageous to heat the carrier to a temperature of from300 to 1000 C. prior to coating, i.e., after priming.

The composition which is used to coat the catalyst and which in the drystate should contain 1 to 15% by weight of vanadium pentoxide and to 99%by weight of titanium dioxide, is prepared by conventional methods. Forexample finely divided titanium dioxide may be soaked with a solution ofa vanadium compound in water or an organic solvent, such as forma-mide,molten thiourea or a monohydric or polyhydric alcohol, so as to producea paste of more or less honeylike consistency. Ammonium thiocyanate orother readily fusible and readily volatile salts may also be used aspasting agents.

Coating the carrier with the active composition is also carried out byconventional methods, for example in a coating drum, with the gradualaddition of the paste, advantageously while simultaneously effectingdrying with hot air. Coating may also be elfected by mixing the carrier,finely divided titanium dioxide and vanadium compound in a coating drumtogether with a fusible organic substance at a temperature above themelting point of the said organic substance. It is advantageous to usea. temperature range of from 80 to 150 C. The active composition is usedin an amount which is necessary to cover the carrier with a layer havinga thickness of 0.02 to 2 mm., particularly 0.05 to 1 mm., the finishedeatalyst containing 0.05 to 3%, preferably 0.1 to 2%, particularly 0.1to 1%, by weight of vanadium pentoxide. To consolidate the coating, itis advantageous to heat the catalyst for some time, for example abouthalf to ten hours, in a current of air at elevated temperature, forexample 200 to 600 C., until organic substances are burnt.

The catalyst coating may consist of vanadium pentoxide and titaniumdioxide in the said amounts, or in addition to vanadium and titanium,may contain small amounts of silver, iron, cobalt, nickel, chromium,molybdenum and/or tungsten, particularly in the form of oxides orhydroxides. These metals are advantageously used in an amount of 0.1 to3% by weight with reference to the catalyst coating.

The oxidation reactions are carried out by conventional methods, i.e.,in the gas phase using oxygen-containing gases or oxygen, atatmospheric, subatmospheric or superatmospheric pressure and attemperatures of from 250 to 600 C.

The invention is illustrated by the following examples.

EXAMPLE 1 188 g. of finely divided titanium dioxide is added to asolution of 28 g. of vanadyl oxylate in a mixture of 30 g. of formamideand 60 g. of water and stirred into a paste. The paste is graduallyintroduced into a coating drum containing 1200 cc. of unglazed porcelainspheres having a diameter of 5 mm., while hot air is passed in at thesame time, until the thickness of the layer is 0.09 mm. The spherescoated with the composition are then heated in a mufile furnace for twohours at 250 C. The finished catalyst contains 3.2% of activecomposition and the content of vanadium pentoxide is 0.19%.

1100 cc. of the catalyst thus prepared is placed in a vertical tubehaving an internal diameter of 25 mm. which is heated in a salt bath.The height of the filling is 2.50 meters. 140 g. per hour of 98%o-xylene in vapor phase is passed over this catalyst layer mixed with3500 liters per hour of air at 400 C. 154.4 g. of phthalic anhydride isobtained per hour in addition to 9.2 g. of maleic anhydride. Calculatedon pure o-xylene, the yield by weight of phthalic anhydride is 112.5%.The theoretical yield is 80.5%.

A similar result is achieved with a catalyst which has been prepared inan analogous way and whose coating also contains 0.2% by weight ofsilver oxide and 0.1% by weight of nickel oxide.

Very good results are also obtained with a catalyst, prepared in ananalogous way, whose coating contains 0.4% by weight of chromium oxidein addition to the said amounts of titanium dioxide and vanadiumpentoxide.

EXAMPLE 2 Fused aluminum silicate is reduced to a particle size of 0.2to 0.5 mm. The particles are shaped into spheres and sintered so that apore-free surface is formed. The diameter of the spheres is 6.5 mm.

16 g. of vanadyl oxylate is dissolved in 30 cc. of formamide at 120 C.This solution is stirred with 106 g. of anatase to form a thick paste.This is brushed onto a plate to a thickness of about 0.5 mm. 290 g. (300cc.) of the said spheres are lightly rolled on the plate so that the 4surface of the spheres is coated with the active composition. Thespheres are then dried and heated in a muffie furnace at 250 C. Thethickness of the layer of active material is 0.2 mm. The finishedcatalyst contains 8.8% of active composition and the content of vanadiumpentoxide is 0.53.

The spheres thus prepared are placed in a tube cm. in length having aninternal diameter of 25 mm. The tube is heated in a salt bath. At atemperature of 390 C., 42 g. of 98% o-xylene in vapor phase and 1000liters of air are passed over the catalyst per hour. 46.2 g. of phthalicanhydride in addition to 2.7 g. of maleic anhydride are obtained perhour. Calculated on pure o-xylene, the yield by weight on phthalicanhydride is 111.3%. The theoretical yield is 79.8%.

A similar result is achieved with a catalyst prepared in an analogousway whose coating, besides the amounts of titanium dioxide and vanadiumpentoxide, contains 1.0% by weight of tungsten oxide or 0.7% by weightof tungsten oxide, 0.15% by weight of iron oxide and 0.15 by weight ofcobalt oxide.

EXAMPLE 3 2000 g. of magnesium silicate spheres are used which have abulk density of 1.51 g./cc., a diameter of 6.6 mm. and which for betteradhesion of the active layer have been slightly etched with concentratedhydrofluoric acid at room temperature for about three minutes. Thespheres which are placed in a heated cotaing drum are coated with apaste of 32 g. of vanadyl oxalate, 50 g. of formamide, 60 g. of waterand 212 g. of titanium dioxide until the thickness of the layer is 0.1mm. The spheres, coated with 96 g. of the active composition, are heatedat 400 C. in a mufile furnace for two hours. The finished catalystcontains 4.6% of active composition and 0.28% of vanadium pentoxide.

At a temperature of 380 C., 4000 liters of air and 164 liters of 98%o-xylene in vapor phase are passed per hour in a tube as in Example 1over 1170 cc. of the catalyst thus prepared. 179.9 g. of phthalicanhydride in addition to 9.6 g. of maleic anhydride are obtained perhour. The yield by weight, calculated on pure o-xylene, is 111.8%. Thetheoretical yield is 80%.

EXAMPLE 4 7 g. of titanium tetrachloride is dissolved in 20 cc. of

glacial acetic acid while cooling. The solution formed is uniformlydistributed onto 250 cc. of fused aluminum oxide having a particle sizeof 4 to 6 mm. in a drum. The carrier thus treated is dried in a currentof air. The glossy coating is then fixed by heating for two hours in amuflle furnace at 400 C. The carrier which has been thus pretreated isbrought into contact with a paste which has been prepared from asolution of 40 g. of vanadyl oxalate in 40 cc. of formamide and 75 cc.of water with the addition of 270 g. of anatase. The excess paste isremoved by shaking on a screen and the catalyst is first heated slowlyto 200 C. and then heated for five hours at 400 C. in a muffle furnace.It contains 5% of active composition and has a content of 0.5% ofvanadium pentoxide.

The finished catalyst is placed in a vertical tube having a length of 80cm. and an internal diameter of 25 mm. which is heated in a salt bath.41 g. of 98% o-xylene and 1100 liters of air are passed per hour overthe catalyst at 400 C. 42.2 g. of phthalic anhydride in addition to 3.5g. of maleic anhydride is obtained per hour. Calculated on pureo-xylene, the yield by weight of phthalic anhydride is The theoreticalyield is 75.1%.

EXAMPLE 5 250 cc. of porcelain spheres having a diameter of 5 mm. arewetted with a solution of 20 g. of vanadyl oxalate in 10 g. of formamideand 10 g. of urea by shaking in a vessel and then heated at 200 C. untilthe solvent has evaporated. The spheres are then heated for thirtyminutes at 700 C. in a muffle furnace. This procedure is repeated sothat the porcelain spheres are coated with a layer of 0.4% by Weight ofvanadium pentoxide.

The carier pretreated in this way is then coated with a paste ofvanadium oxalate and titanium dioxide as described in Example 4. Thefinished catalyst contains 3.3% of active composition. The total contentof vanadium pentoxide is 0.49%.

In the oxidation of o-xylene under the conditions described in Example 4the catalyst yields at 410 C. 45.7 g. of phthalic anhydride and 2.8 g.of maleic anhydride per hour. The yield of phthalic anhydride by weightis 113.6% with reference to pure o-xylene. The theoretical yield is81.5%. The yield by weight is 112.5% when the porcelain spheres are notpretreated with vanadium pentoxide. If the spheres be pretreated with asolution of iron acetate and chromium acetate in an analogous way sothat they have a priming of 0.2% by weight of chromium oxide and 0.2% byweight of iron oxide, and then coated in the manner described above withtitanium dioxide and vanadium pentoxide, a yield of 113.4% by weight ofphthalic anhydride is achieved in the oxidation of o-xylene.

EXAMPLE 6 5 g. of molybdic acid is idssolved in a mixture of 8 cc. ofet'hanolamine, 2 cc. of water and 10 g. of urea and made up to cc. With'formamide. 469 g. of steatite spheres having a diameter of 5.5 mm. arewetted with 10 cc. of the said solution by shaking, dried at 200 C. andheated in a mufile furance for fifteen minutes at 830 C. The amount ofmolybdic acid applied amounts to 0.7 g. The spheres thus pretreated arecoated as described in Example 4 with the active vanadium oxalate/titanium dioxide composition, dried and heated for four hours in amufiie furnace at 400 C. The finished catalyst contains 5.8% of activecomposition and 0.35% of vanadium pentoxide.

In the oxidation of o-xylene at 410 C., the catalyst thus preparedyields (under the conditions of Example 4) 250 cc. of magnesium silicatespheres having a diameter of 5.5 mm. are coated in a heated coating drumwith a paste which has been prepared from 106 g. of titanium dioxide, 16g. of vanadyl oxalate, 1.4 g. of ammonium molybdate, g. of formamide andg. of Water, until there is 26 g. of the composition on the spheres. Thespheres are then heated in a mufile furnace for two hours at 450 C. 1000liters of air and 44.7 g. of 98% o-xylene at 390 C. are passed per hourover the catalysts thus prepared. 49.7 g. of phthalic anhydride and 1.9g. of maleic anhydride are obtained per hour.

With reference to pure o-xylene, the yield by weight of phthalicanhydride is 113.5%. The theoretical yield is 81.2%.

We claim:

1. A catalyst containing vanadium and titanium for the oxidation ofaromatic hydrocarbons or unsaturated aliphatic hydrocarbons intocarboxylic acids or carboxylic acid anhydrides, said catalyst comprisingan inert nonporus carrier having a mean particle size of at least about2 mm. coated with a layer of a composition 0.02 to 2 mm. thick whichconsists essentially of 1 to 15% by weight of vanadium pentoxide and to99% by weight of titanium dioxide, the catalyst having a content ofvanadium pentoxide of from 0.05 to 3% by weight.

2. A catalyst as claimed in claim 1 wherein the inert nonporus carrierhas a surface area of less than 3 sq. in. per gram.

3. A catalyst as claimed in claim 1 wherein-the inert nonporous carrierhas a mean particle size of 2 to10 mm.

4. A catalyst as claimed in claim 1 whose carrier is pretreated with 0.5to 1.5% by weight of at least one oxide of the metals vanadium,molybdenum, tungsten, chromium, titanium or iron, prior to being coatedwith the vanadium pentoxide/titanium dioxide composition.

5. A catalyst as claimed in claim 1 whose composition used as a coatingcontains not only vanadium pentoxide and titanium dioxide, but also atleast one oxide of the metals silver, iron, cobalt, nickel, chromium,molybdenum and tungsten in an amount of 0.1 to 3% by weight withreference to the composition used as coating.

6. A catalyst as claimed in claim 1 whose carrier has a surface area of0.005 to 2 sq. m/ g.

7. A catalyst as claimed in claim 1 whose carrier is in the form ofspheres.

8. A catalyst as claimed in claim 1 consisting essentially of 1 to 15 byweight of vanadium pentoxide and 85 to 99% by weight of titanium dioxidecoated to a thickness of about 0.05 to 1 mm. on said inert nonporouscarrier which has a surface area of about 0.005 to 2 sq. m./gram, thecontent of vanadium pentoxide in said catalyst being about 0.1 to 2% byweight.

9. A catalyst as claimed in claim 8 wherein the content of vanadiumpentoxide in said catalyst is about 0.1 to 1% by weight.

10. A catalyst as claimed in claim 8 wherein said carrier is coated witha single layer of the vanadium pentoxide/ titanium dioxide compositionwhich contains up to 3% by weight thereof of at least one oxide of ametal selected from the group consisting of silver, iron, cobalt,nickel, chromium, molybdenum and tungsten.

11. A catalyst as claimed in claim 8 wherein said carries is precoatedwith a first layer of 0.05 to 1.5% by weight thereof of at least oneoxide of a metal selected from the group consisting of vanadium,molybdenum, tungsten, chromium, titanium and iron with a second layer ofsaid vanadium pentoxide/titanium dioxide applied thereover as a secondlayer.

References Cited UNITED STATES PATENTS 2,510,803 6/1950 Cooper 252-4642,698,306 12/1954 Matejczyk 252-464 3,055,842 9/1962 Robinson 252-4613,215,644 11/1965 Kakinoki et al 252-461 DANIEL E. WYMAN, PrimaryExaminer P. N. FRENCH, Assistant Examiner U.S. Cl.X.R.

